Valve drive devices are already known which have a means for switching the stroke of gas exchange valves. The invention is based on a valve drive in which the gas exchange valves, in particular inlet valves and outlet valves of an internal combustion engine, are actuated directly or indirectly by means of a camshaft. For switching the valve stroke, cams which are adjacent on the camshaft are provided with different cam shapes, which are combined to form a cam unit. By axially displacing the cam units on the camshaft, the stroke of the gas exchange valves is altered in accordance with the contour of the cams. For the displacement of the cam units, an adjustment shaft which extends parallel to the camshaft is provided with corresponding elements for engagement on the cam units.
DE 10 2009 037 268 B3 discloses a variable valve drive for actuating gas exchange valves for internal combustion engines, in which the camshaft is constructed from a plurality of individual cam sleeves which can be displaced relative to one another. The cam sleeves, which are positioned side by side, are interconnected by means of an axially extending toothing, in that the toothings of adjacent cam sleeves engage in one another. On each cam sleeve, a plurality of different cam profiles having the same base circle are provided side by side, and can be brought into engagement with the respective gas exchange valve in succession by way of the axial displacement of the cam sleeves, and thus result in different actuations of the gas exchange valve. For the axial displacement of the cam sleeves, a switching shaft, which is mounted so as to be rotatable but axially undisplaceable relative to the camshaft, is arranged in the interior of the camshaft and is operatively connected to the cam sleeves by means of a switching ball, and the switching ball on the one hand is mounted so as to be fixed in position in the cam sleeve and on the other hand runs in a switching contour on the switching shaft. The switching contour has an axial inclination, in such a way that the cam sleeves are axially displaced when the switching shaft is rotated relative to the camshaft, and it is thus possible to switch between the different cam profiles of a cam sleeve so as to actuate the respective gas exchange valve.
DE 10 2009 039 733 A1 discloses a valve drive for gas exchange valves of an internal combustion engine, in which a cam unit, comprising a plurality of different cam paths which are arranged side by side, is mounted on a camshaft so as to be rotationally engaged and axially displaceable, and the cam unit is axially displaceable by means of an adjustment means. The adjustment means comprises an adjustment element, which is mounted so as to be movable inside the camshaft, for transmitting the adjustment movement to the cam unit. For this purpose, the adjustment element comprises on the circumference thereof a running path profile, which cooperates with a coupling element, and the coupling element is further connected to the cam unit through a clearance in the camshaft. Moving the adjustment element relative to the camshaft brings about an axial displacement of the cam unit on the camshaft. As a variant embodiment, it is disclosed that the adjustment element is mounted so as to be rotatable in the camshaft, and that the running path profile extends substantially in the circumferential direction on the adjustment element. The change between two cam paths on the cam unit for the actuation of the gas exchange valves is achieved by way of an axial offset in the running path profile, which results from a rotation of the adjustment element relative to the camshaft.